1. Field of the Invention
This invention relates to a method and apparatus of ultrasonic flaw detection, and more particularly to a method and apparatus capable of high-speed judging of the harm caused by defects which includes detecting the directions, inclinations, sizes and depths of cavern voids or other internal flaws of various materials.
2. Description of the Prior Art
Cast stocks sometimes contain oblique cavern voids due to a spout of gases which take place in the casting stage. In this connection, few attempts have ever been made to analyze the shape of an internal defect in terms of determining its harmfulness to the strength of a material intended for a specific use, except simple definitions of harmfulness by the dimensions of a defect as projected on the surface. However, in view of the particular directionality of the stress to be applied on the material, the harmfulness of a cavern void of a given size normally varies depending upon whether it extends in X-direction or Y-direction. From the standpoint of the strength of a material, the allowable defect size in X-direction of a material differs from that of Y-direction. Under these circumstances, it is a matter of utmost importance to detect the shaped (directions, inclinations and sizes) of internal cavern defects with accuracy.
For the detection of internal defects as mentioned above, the so-called ultrasonic methods have been utilized in which an ultrasonic pulse is transmitted into a material to receive the echoes from the internal defects. However, the conventional ultrasonic methods in which the ultrasonic pulses are transmitted and received through a single probe or a plural number of probes which are scanned along the surface in predetermined directions in an inspection zone of a material, can display only the position and roughly estimated size of the defects which are calculated from very limited information such as the propagation time and direction of the refraction angle and the amplitude of the ultrasonic pulse on a display medium and therefore the conventional ultrasonic methods can hardly determine the shapes (directions, inclinations and sizes) of the crosswise (inclined) cavern defects.
In order to solve this problems, the present inventors developed a method which employs a revolving inclined probe to transmit and receive the ultrasonic pulse in a direction intersecting a rotational axis in an inspection zone of a material under inspection. The probe is turned through 360.degree. about the rotational axis while transmitting and receiving ultrasonic pulses, and indicating the peak values of echoes received at the flaw detection gate as a detected flaw pattern on a display medium for judging therefrom the direction, inclination, size and depth of the detected defect. This method has a great advantage over the above-mentioned conventional methods in that it is capable of accurately determining the shapes of internal defects such as the directions, inclinations and sizes thereof. However, the inventor' prior method has a drawback in that it takes a long time to detect the depth of a defect by a single probe, since the same operation has to be repeated a number of times, varying the depth of inspection each time. Further, the above-mentioned methods all rely on the operator with regard to the judgement of the harmfulness of a detected defect, which is relatively easy in the flaw detection of a small piece of material but difficult to adopt in the on-line flaw detection of large materials.